Wearable devices, such as wear-and-forget health monitoring systems, should ideally be imperceptible. To this end, they preferably conformal to the contours of the skin, self-adhering, ultra-lightweight, and translucent. Existing synthetic ultra-thin polymers possess some of these traits, but in turn present issues of breathability and biocompatibility. The lack of water permeability in these materials prevents chemical contact between the electronics on the substrate and the underlying epidermal layer. Thus, synthetic polymers have limited utility for health applications and struggle to pass biocompatibility protocols.
In a biomaterials context, bio-derived materials, such as silk or fibroin, can be processed in solution form and have potential in niche biomedical applications. These materials, however, rapidly degrade, have poor gas barrier properties, are costly to manufacture, and currently can only form thick sheets due to poor mechanical stability.
For health-related conformal electronics, patterned substrates attuned to specific parts of the body are required. The formation of patterned, freestanding structures in thin films using masked dry etching techniques has been established in synthetic organic films, such as resins (e.g., photoresists), epoxies (e.g., SU-8), polymers (e.g., polyamide) and small molecules (e.g., perylene). These techniques have been mainly limited to microelectromechanical systems (MEMS) and membrane fabrication. Moreover, such freestanding structures are not isolated, as they typically are anchored to a substrate, require an additional backing layer, or are clamped into enclosed spaces.
A need exists for techniques to pattern nanocellulose structures.